Binary circuits are extensively used in computer systems to carry out instructions and arithmetical processes. Any logical procedure may be effected by using a suitable combination of basic logic gates. Thus, logic circuits are building blocks of computer systems. And, CMOS is often the preferred technology for such logic circuits.
There are two commonly recognized methods of logic circuit design: static and dynamic. Dynamic refers to any device or circuit in which the signals decay over a period of time unless regenerated. The CMOS random access memory is a particular example of this type of device. Any component, circuit, or device that is not dynamic or that is operated with essentially constant electrical conditions is described as static.
To meet the demand for higher performance microprocessors, the above design techniques must inevitably evolve. Meeting performance requirements is usually accomplished by using high speed dynamic circuits along critical paths. However, the dynamic circuit design has the following disadvantages when compared to a static circuit design, regardless of whether the dynamic design is self-resetting (as in a SR-CMOS logic circuit), or clocked pre-charged (as in domino logic circuitry):
1. Higher power consumption; PA1 2. External reset generation requirement; PA1 3. Complicated reset timing requirement; PA1 4. Power-On Reset ("POR") signal required to initialize circuit; PA1 5. Overhead circuitry needed for conversion of dynamic to static-like behavior during test mode.
Thus, to obtain maximum speed performance, dynamic circuit design techniques must sacrifice the robustness attainable from a static circuit. However, in spite of the robustness and lower power dissipation of static circuits, they experience current overlap during a state transition, which unnecessarily dissipates power and reduces speed.
Therefore, there is a need in the art for a logic circuit design that combines the advantages of static and dynamic design techniques, but avoids many of their respective disadvantages.